Question

A uniform magnetic field of magnitude 0.166 T is directed along the
positive x axis. A positron moving at a speed of 4.85 106 m/s
enters the field along a direction that makes an angle of ? = 85.0°
with the x axis (see figure below). The motion of the particle is
expected to be a helix. Calculate the pitch p of the trajectory
(helix)?
the pitch is 9.1810^-5m, what is theradius of the trajectory?